After four fatal accidents involving Amtrak trains in the last two months, including one that left a train dangling off an overpass and one that led to a spill of 5,000 gallons of diesel fuel, questions are growing about how safe the nation’s railways are for passengers and motorists.

On Tuesday, an Acela Express train carrying dozens of passengers decoupled north of Baltimore while it was traveling at up to 125 miles per hour. Though the decoupling caused no injuries, it followed a particularly rocky eight weeks for the passenger rail service.

Days earlier, an Amtrak train collided with a parked freight train in Cayce, South Carolina after it was diverted to the wrong track, killing its engineer and conductor. Officials say it could take months to clean up a fuel spill caused by the crash.

The previous Wednesday, a train carrying Republican members of Congress to a retreat in West Virginia crashed into a garbage truck on the track in Crozet, Virginia. The driver of the truck was killed and many other people were injured.

In Nash County, North Carolina on January 14, a pastor and his wife were killed when their SUV was hit by an Amtrak train traveling from New York to Georgia. Police do not know why she drove around a lowered crossing arm onto the tracks.

On December 18, a train headed from Seattle to Portland hit a curve too fast and derailed near DuPont, Washington. Four cars went off the track onto a highway below. Three passengers were killed, 62 others on the train were injured, and eight people on the highway were also hurt. Damage was estimated at more than $40.4 million. Amtrak said in a statement at the time that it was saddened by the loss of life and the injuries, but it was awaiting the results of an investigation.

“The investigation will be conducted by the National Transportation Safety Board, and we will cooperate fully with all authorities. At this time, we will not speculate about the cause, and we encourage others not to speculate as well,” Amtrak said.

Richard Beall, a railroad operation and safety consultant and former locomotive engineer, stressed that it is unfair to lump all of these cases together as “Amtrak problems.”

“It’s more complicated than that,” he said.

NTSB investigations can take months or even years to complete, so definitive answers are not yet available for any of these crashes. Preliminary findings do indicate likely causes, though, and most of these accidents involved external factors.

It appears at this point that incidents in North Carolina and Virginia were not the fault of the train operator or the railroad, but rather cases of drivers going around gates and trying to cross in front of the train.

“Number one, not Amtrak’s fault,” said Allan Zarembski, a professor and director of the Railroad Engineering and Safety Program at the University of Delaware. “Number two, nothing Amtrak can do.”

In South Carolina, the train was traveling on track owned by CSX, and it was directed onto the wrong stretch of track by a switch that had been manually set. Amtrak owns and maintains very little of the track it travels on outside the northeast, and it is dependent on the private railway owners elsewhere.

“If the cause was having to do with the track or having to do with the switching, that’s out of Amtrak’s control,” Zarembski said.

In the December crash, though, an Amtrak engineer missed a milepost marker and sped into a curve at 50 miles per hour above the speed limit. According to a preliminary report, the engineer told investigators he intended to begin braking a mile before the curve, but he mistook a signal and thought he was further away than he was.

The derailment occurred on the inaugural run of Amtrak’s new Point Defiance Bypass route, and engineers and conductors told CNN they had concerns about safety and inadequate training. The engineer on the train told the NTSB he only had one training run at the controls heading in the direction the train was traveling.

"Our highest priority is ensuring the safety of our passengers, our crew and the communities we serve. We are actively taking measures to strengthen the safety of our operations,” Amtrak said in a statement last week.

Taking into account what is known about all of these cases, railroad engineering expert Augustine Ubaldi said the frequency of accidents over the last two months is likely coincidental.

“Washington was maybe overspeed, vehicle collisions appear to be the result of drivers failing to heed crossing warnings, and South Carolina may be a failure of the CSX freight train crew, the CSX dispatcher, or the Amtrak engineer,” he said. “Consider how many Amtrak and freight trains have traveled safely in that time.”

Rep. Kyle Mooney, R-W.V., said it is difficult to prescribe solutions without a full understanding of the facts, but warnings at railway crossings must be taken seriously.

“Maybe some education that [drivers] don’t try to go around the gates and speed through,” he said. “We’re still waiting for the report, so I don’t want to say something that might not be accurate. But when trains come and you hear the sign, the gates go down…you have to be patient and wait.”

Other updated safety measures may be needed as well.

“I’m all for the train system,” Mooney said. “Obviously we need to make sure we’re modernized, if there’s cameras to look out in advance, make sure that we have safety precautions.”

The rate of accidents per million miles of railroad for Amtrak has risen from 41.1 in 2008 to 58.7 for the first 11 months of 2017 (the December Washington derailment is not yet factored in). Total fatalities have gone from 119 in 2008 to 167 in 2017. However, the vast majority of those deaths, 103 in 2017, were trespassers, and most of the rest were highway-rail accidents.

Only 12 deaths involved passengers on trains in 2017, not including the three killed in the December derailment. Train accidents not involving road crossings, derailments, and incidents caused by track or equipment defects have all dropped significantly over the last 10 years.

Trains hitting vehicles are not uncommon and generally do not make national news, but a crash involving most of the Republicans in Congress or a train car careening off a bridge draws the public’s attention. The less severe incidents suddenly become more noteworthy.

“Everybody jumps on them,” Zarembski said. “Then of course once you’re watching for Amtrak accidents, you see everything.”

Congress has mandated that all railroads install a system called positive train control by the end of 2018. The GPS-based system can automatically apply brakes or alert an engineer of problems. The NTSB says PTC could have prevented many of the crashes it has investigated over the last 50 years that resulted in hundreds of deaths and thousands of injuries.

“It will solve, for instance, the one in Washington state,” Beall said, “It would have definitely done something about that.”

It is expensive to install, though, and implementation has been slow in many areas. According to media reports, the track where the South Carolina crash occurred was operating on manual signals because it was in the process of being upgraded to PTC.

Although pressure from the rail industry convinced Congress to extend the original deadline in 2015, Transportation Secretary Elaine Chao has notified railroads that they should not expect another extension this year.

“We are concerned that many of the nation’s railroads must greatly accelerate their efforts to achieve the congressionally mandated requirements,” she said in a letter to executive officers at the 37 railroads required to install the systems.

PTC is far from a silver bullet, though. Only a fraction of accidents would be prevented by it, although they would be some of the more high-profile ones.

“Industry estimates put it at 2 percent,” Ubaldi said.

Derailments caused by track or equipment defects would not be affected, for example, and funds used to install the technology might otherwise be spent improving infrastructure.

“There’s always been an ongoing argument about whether that money is being diverted from something else,” Zarembski said.

Options for discouraging drivers from attempting to cross tracks without creating additional risks are limited. Installing harder to evade barriers could inadvertently trap vehicles on the tracks.

Operation Lifesaver, a national rail safety non-profit organization, attempts to educate the public about the dangers.

“Our state programs and trained volunteers provide free presentations to show people how to make safe choices at railroad crossings and along rights-of-way,” the group said in a statement Thursday. “We teach citizens that it is illegal to be on railroad tracks except at a designated crossing, and that driving or walking around lowered crossing gates or disregarding flashing crossing signals also is illegal and dangerous.”

Operation Lifesaver encourages pedestrians to remain alert around tracks and advises drivers to never try to cross if a train is coming or a gate is down.

Amid all of these accidents, the top job at the Federal Railway Administration remains unfilled with a nominee blocked by Democratic senators fighting for federal funding for a Hudson River tunnel project.

Deputy Secretary of Transportation Jeff Rosen complained about the vacancy in a letter to Senate Minority Leader Chuck Schumer in the wake of the Virginia crash last week, urging him to lift his hold on the nomination “in the interest of public safety.”

Democrats say the nominee, Ron Batory, is already working fulltime at the FRA without confirmation, but Republicans argue his authority and ability to make decisions is limited. According to Schumer, the Obama administration approved funding for half of the $29 billion Gateway Program, but a department official told NBC they have been unable to locate a copy of that agreement.

In its budget proposal last year, the Trump administration called for cutting Amtrak’s subsidies from $1.4 billion to $630 million, citing poor performance and lack of profits. Experts say reducing federal funds will not address either of those problems.

According to Zarembski, Amtrak recuperates much of its operating costs, but it still needs federal subsidies to cover costs of equipment and maintenance. He noted that many more highly-regarded rail systems abroad also lose money, but their governments see benefits in encouraging rail travel over driving.

“Amtrak is a passenger system.... Passenger systems do not make money,” he said. “Passenger systems are like any other infrastructure.”

Beall suspects some in D.C. advocate cutting Amtrak funding because they want it to fail so it can be shut down and more profitable private freight operations can dominate the railways.

“Other countries put their money into the systems,” Beall said. “Ours seems to take it away from them.”